APOD: Orbits of Potentially Hazardous... (2021 Aug 29)

[APOD Robot]

Orbits of Potentially Hazardous Asteroids

Explanation: Are asteroids dangerous? Some are, but the likelihood of a dangerous asteroid striking the Earth during any given year is low. Because some past mass extinction events have been linked to asteroid impacts, however, humanity has made it a priority to find and catalog those asteroids that may one day affect life on Earth. Pictured here are the orbits of the over 1,000 known Potentially Hazardous Asteroids (PHAs). These documented tumbling boulders of rock and ice are over 140 meters across and will pass within 7.5 million kilometers of Earth -- about 20 times the distance to the Moon. Although none of them will strike the Earth in the next 100 years -- not all PHAs have been discovered, and past 100 years, many orbits become hard to predict. Were an asteroid of this size to impact the Earth, it could raise dangerous tsunamis, for example. To investigate Earth-saving strategies, NASA's Double Asteroid Redirection Test (DART) is planned for launch later this year. Of course rocks and ice bits of much smaller size strike the Earth every day, usually pose no danger, and sometimes creating memorable fireball and meteor displays.

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[Ann]

Orbits of Potentially Hazardous Asteroids.
Image Credit: NASA, JPL-Caltech

Rain in Malmö. Photo: Johan Nilsson.

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It's a downpour! Open your umbrellas!

Ann

[revloren]

Some of the tracks seem more predominant than the background. Specifically the one at upper right that goes inside the orbit of Mercury and out past the hypothetical Mars. Just more of a unique, perhaps unstable orbit?

[xuxu]

That pic is proof we need to be doing more to track ,deflect or destroy any of those that may hit us today or tomorrow.
Great post.

[neufer]

Some of the tracks seem more predominant than the background. Specifically the one at upper right that goes inside the orbit of Mercury and out past the hypothetical Mars. Just more of a unique, perhaps unstable orbit?

https://www.syfy.com/syfywire/meet-2021 ... known-year

<<2021 PH₂₇ is a near-Earth asteroid of the Atira group. It was discovered by Scott Sheppard using the Dark Energy Survey's DECam imager at NOIRLab's Cerro Tololo Inter-American Observatory on 13 August 2021. 2021 PH₂₇ has the smallest semi-major axis and shortest orbital period among all known asteroids as of 2021. With an absolute magnitude of 17.7, the asteroid is expected to be larger than 1 km in diameter.

2021 PH₂₇ was discovered by astronomer Scott Sheppard using the Dark Energy Survey's DECam imager at Cerro Tololo Observatory in Chile on 13 August 2021. The observations were conducted at twilight to search for undiscovered minor planets situated at low elongations from the Sun. The object was discovered at apparent magnitude 19, with a solar elongation of 37 degrees. It was then reported to the Minor Planet Center's Near-Earth Object Confirmation Page under the temporary designation v13aug1. Over five days, follow-up observations were conducted by various observatories including Las Campanas (304), Las Cumbres (K91, W85, W87, Q63), SONEAR (Y00), and iTelescope (Q62). The object was then provisionally designated 2021 PH₂₇ by the Minor Planet Center and announced on 21 August 2021. Even in April 2021, the asteroid was never more than 45 degrees from the Sun.

Oblique view of 2021 PH27's orbit compared to the inner planets

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2021 PH₂₇ orbits the Sun at a distance of 0.13–0.79 AU once every 4 months (114 days; semi-major axis of 0.46 AU). Its orbit has an eccentricity of 0.71 and an inclination of 32 degrees with respect to the ecliptic. It is classified as a near-Earth object (NEO) due its perihelion distance being less than 1.3 AU. It also falls under the NEO category of Atira asteroids, whose orbits are confined entirely within Earth's orbit at 1 AU from the Sun. Its orbit crosses the paths of Mercury and Venus, with nominal minimum orbit intersection distances of 0.11 AU and 0.015 AU, respectively.

As of 2021, 2021 PH₂₇ holds the record for the smallest semi-major axis (0.46 AU) and shortest orbital period (114 days) of any known asteroid, supplanting 2019 LF6 and 2020 AV2 (0.56 AU, 151 days). For comparison, Mercury has a semi-major axis of 0.39 AU and an orbital period of 88 days. Being so close to the Sun, at perihelion the asteroid is moving at 106 km/s.

With an observation arc of only 5 days, the orbit quality of 2021 PH₂₇ is poor, with a high uncertainty parameter of 9. Additional observations are necessary to constrain uncertainties in its orbit by the time the asteroid approaches perihelion and enters conjunction with the Sun in October 2021, during which it will become unobservable at solar elongations less than 20 degrees. After 2021 PH₂₇ exits conjunction in 2022, its positional uncertainty will have grown up to several thousands of arcseconds, which will render it a lost minor planet. It currently comes closer to Venus than any of the other planets.>>

[Chris Peterson]

Some of the tracks seem more predominant than the background. Specifically the one at upper right that goes inside the orbit of Mercury and out past the hypothetical Mars. Just more of a unique, perhaps unstable orbit?

The orbits of every body in the Solar System can be seen as unstable. But those of small bodies in planet crossing orbits are especially so, being frequently perturbed.

[Chris Peterson]

That pic is proof we need to be doing more to track ,deflect or destroy any of those that may hit us today or tomorrow.
Great post.

Your chance of dying from an asteroid impact is similar to your chance of dying in a commercial airplane crash. We spend a lot of money trying to prevent the latter. Not so much the former.

[orin stepanek]

Kinda looks like somebody got really into his Spirograph!
Seriously I'm glad they are being tracked; even so we don't see them all!

[Eclectic Man]

The image shows the eccentricities of the orbits of the inner planets quite well.

Mercury has an eccentricity of 0.206, which is the greatest after Pluto (0.248) (yes, I know Pluto's designation is 'controversial'*). Venus' orbit (eccentricity 0.007) is less eccentric than our own on planet Earth (0.017) and Neptune is only slightly more eccentric than Venus at 0.009. The others are Mars, 0.093; Jupiter, 0.048; Saturn, 0.056; and Uranus, 0.047.

https://www.enchantedlearning.com/subje ... city.shtml

I wonder how eccentric an orbit could be for a planet to retain the potential to support life. Is orbiting in the 'Goldilocks' zone enough, or does a planet have a better chance of supporting life teh closer to circular its orbit is? (Oe for the astro-biologists.)

*https://www.forbes.com/sites/jamiecarte ... this-week/

[Chris Peterson]

The image shows the eccentricities of the orbits of the inner planets quite well.

Mercury has an eccentricity of 0.206, which is the greatest after Pluto (0.248) (yes, I know Pluto's designation is 'controversial'*). Venus' orbit (eccentricity 0.007) is less eccentric than our own on planet Earth (0.017) and Neptune is only slightly more eccentric than Venus at 0.009. The others are Mars, 0.093; Jupiter, 0.048; Saturn, 0.056; and Uranus, 0.047.

https://www.enchantedlearning.com/subje ... city.shtml

I wonder how eccentric an orbit could be for a planet to retain the potential to support life. Is orbiting in the 'Goldilocks' zone enough, or does a planet have a better chance of supporting life teh closer to circular its orbit is? (Oe for the astro-biologists.)

I'll bet the Goldilocks zone is lot wider than commonly accepted. That life can exist in a very wide range of conditions, including on planets with very eccentric orbits. Where I think stability matters is for complex life.

[E Fish]

That pic is proof we need to be doing more to track ,deflect or destroy any of those that may hit us today or tomorrow.
Great post.

We already know what to do. We just need to send Bruce Willis into space to set off a nuke. Nukes fix everything.

More seriously, this is an interesting amalgam of orbits, and when you consider how many millions of asteroids there are, the idea of being able to trace even a significant number of them seems like an impossible task.

[neufer]

That pic is proof we need to be doing more to track ,deflect or destroy any of those that may hit us today or tomorrow.

Your chance of dying from an asteroid impact is similar to your chance of dying in a commercial airplane crash. We spend a lot of money trying to prevent the latter. Not so much the former.

The chance of a single person born today dying due to an impact ~1 in 200,000.
The chance of a single person ... dying in a commercial airplane crash ~1 in 200,000.

Air accident fatalities recorded by ACRO 1918–2018

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<<The late Eugene Shoemaker of the U.S. Geological Survey estimated the rate of Earth impacts, concluding that an event about the size of the nuclear weapon that destroyed Hiroshima occurs about once a year. Such events would seem to be spectacularly obvious, but they generally go unnoticed for a number of reasons: the majority of the Earth's surface is covered by water; a good portion of the land surface is uninhabited; and the explosions generally occur at relatively high altitude, resulting in a huge flash and thunderclap but no real damage.

Although no human is known to have been killed directly by an impact, over 1000 people were injured by the Chelyabinsk meteor airburst event over Russia in 2013. In 2005 it was estimated that the chance of a single person born today dying due to an impact is around 1 in 200,000. The two to four-meter-sized asteroids 2008 TC3, 2014 AA, 2018 LA, 2019 MO, and the suspected artificial satellite WT1190F are the only known objects to be detected before impacting the Earth.>>

[johnnydeep]

Neufer, you're not implying that 2021 PH27 is the same one that caught the eye of xuxu are you? They don't look like they have the same orbit to me:

[johnnydeep]

Now I'm wondering if any of these will impact any of the other planets!

[Chris Peterson]

That pic is proof we need to be doing more to track ,deflect or destroy any of those that may hit us today or tomorrow.

Your chance of dying from an asteroid impact is similar to your chance of dying in a commercial airplane crash. We spend a lot of money trying to prevent the latter. Not so much the former.

The chance of a single person born today dying due to an impact ~1 in 200,000.
The chance of a single person ... dying in a commercial airplane crash ~1 in 200,000.

My numbers come from a very different analysis, looking at the rate of "dinosaur killer" impacts. They are separated by tens of millions of years, but if one were to happen today, several billion deaths would result.

[Chris Peterson]

Now I'm wondering if any of these will impact any of the other planets!

Not many, unless they are perturbed. You'd need a body with a very low inclination such that it actually intersected the orbit of two planets.

[neufer]

Click to play embedded YouTube video.

My numbers come from a very different analysis, looking at the rate of "dinosaur killer" impacts.

They are separated by tens of millions of years, but if one were to happen today, several billion deaths would result.

[dddavids]

If the earth is safe for the next 100 years, then what about Mars and Venus? If there were an impact on one of our neighbors, it would afford many interesting research possibilities.

[neufer]

If the earth is safe for the next 100 years, then what about Mars and Venus?

Click to play embedded YouTube video.

Mojave Crater: 7.5°N 33.0°W / Mars Pathfinder: 19.13°N 33.22°W

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<<Mojave is a 58 km diameter impact crater in the Oxia Palus quadrangle of Mars. The crater is located at 7.5° N and 33.0° W within the Martian Xanthe Terra region. Some parts of the crater display a high concentration of closely spaced pits. Pits show little or no evidence of rims or ejecta. The pits are so close to each other that adjacent pits often share the same wall. It is believed that the pits form from steam produced when the heat from the impact process interacts with ice in the ground. Mojave is a rayed crater, another indication of its youth, and is the largest such crater on Mars. Based on crater counts of its ejecta blanket, it is thought to be about 3 million years old. It is believed to be the most recent crater of its size on Mars, and has been identified as the probable source of the shergottite meteorites collected on Earth.

The depth of Mojave is approximately 2,600 meters. Based on its ratio of depth to diameter, researchers believe it is very young. It is not old enough to have accumulated much material and start to fill. Its relatively undegraded state helps scientists model impact processes on Mars. If one measures the diameter of a crater, the original depth can be estimated with various ratios. Because of this relationship, researchers have found that many Martian craters contain a great deal of material; much of it is believed to be ice deposited when the climate was different.>>

Click to play embedded YouTube video.

<<The high population of the asteroid belt makes for a very active environment, where collisions between asteroids occur frequently (on astronomical time scales). Collisions between main-belt bodies with a mean radius of 10 km are expected to occur about once every 10 million years. A collision may fragment an asteroid into numerous smaller pieces (leading to the formation of a new asteroid family).

Along with the asteroid bodies, the asteroid belt also contains bands of dust with particle radii of up to a few hundred micrometres. This fine material is produced, at least in part, from collisions between asteroids, and by the impact of micrometeorites upon the asteroids. Due to the Poynting–Robertson effect, the pressure of solar radiation causes this dust to slowly spiral inward toward the Sun.

The combination of this fine asteroid dust, as well as ejected cometary material, produces the zodiacal light. Asteroid particles that produce the visible zodiacal light average about 40 μm in radius. The typical lifetimes of main-belt zodiacal cloud particles are about 700,000 years. Thus, to maintain the bands of dust, new particles must be steadily produced within the asteroid belt. It was once thought that collisions of asteroids form a major component of the zodiacal light. However, computer simulations by Nesvorný and colleagues attributed 85 percent of the zodiacal-light dust to fragmentations of Jupiter-family comets, rather than to comets and collisions between asteroids in the asteroid belt. At most 10 percent of the dust is attributed to the asteroid belt.>>

NWA 6963, a shergottite found in Morocco, September 2011.

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<<Roughly three-quarters of all Martian meteorites can be classified as shergottites. They are named after the Shergotty meteorite, which fell at Sherghati, India in 1865. Shergottites are igneous rocks of mafic to ultramafic lithology. They fall into three main groups, the basaltic, olivine-phyric (such as the Tissint group found in Morocco in 2011) and Lherzolitic shergottites, based on their crystal size and mineral content. They can be categorised alternatively into three or four groups based on their rare-earth element content. These two classification systems do not line up with each other, hinting at complex relationships between the various source rocks and magmas from which the shergottites formed.>>

Piece of the Tissint meteorite with glossy black fusion crust & light gray matrix

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Number of asteroids in the asteroid belt as a function of their semi-major axis. The dashed lines indicate the Kirkwood gaps, where orbital resonances with Jupiter destabilize orbits. The color gives a possible division into three zones

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<<On July 18, 2011, around 2 AM local time, a bright fireball was observed by several people in the Oued Drâa valley, east of Tata, Morocco. One observer reported that the fireball was initially yellow in color, then turned green, illuminating the entire area before it appeared to break into two pieces; two sonic booms were heard over the valley. In October 2011, nomads began to find very fresh, fusion-crusted stones in a remote area of the Oued Drâa intermittent watershed. The Tissint meteorite was named after the town of Tissint, 48 kilometres away from the fall site. Dozens of fragments with masses ranging from 0.2 to 1,282 grams were collected, totaling roughly 12–15 kilograms.

The meteorite was ejected from the surface of Mars between 700,000 and 1.1 million years ago. Tissint appears to be derived from a deep mantle source region that was unlike any of the other known Martian shergottite meteorites. The material is highly shocked and indicates it was ejected during the largest impact excavation in record. Given the widely dispersed shock melting observed in Tissint, alteration of other soft minerals (carbonates, halides, sulfates and even organics), especially along grain boundaries, might have occurred. This may in part explain the lack of such minerals in Tissint, but it is unknown if it is of biotic origin.

The meteorite fragments were recovered within days after the fall, so it is considered an "uncontaminated" meteorite. The meteorite displays evidence of water weathering, and there are signs of elements being carried into cracks in the rocks by water or fluid, which is something never seen before in a Martian meteorite. Specifically, scientists found carbon and nitrogen-containing compounds associated with hydrothermal mineral inclusions. One team reported measuring an elevated carbon-13 ratio, while another team reported a low ¹³C ratio as compared to the content in Mars' atmosphere and crust, and suggested that it may be of biological origin, but the researchers also noted that there are several geological processes that could explain that without invoking complex life-processes; for example, it could be of meteoritic origin and would have been mixed with Martian soil when meteorites and comets impact the surface of Mars, or of volcanic origin.

The data on refractory trace elements, sulfur and fluorine as well as the data on the isotopic composition of nitrogen, argon and carbon released upon heating from the matrix and glass veins in the meteorite unambiguously indicate the presence of a Martian surface component including trapped atmospheric gases. So, the influence of in situ Martian weathering can be distinguished from terrestrial contamination in the meteorite. The Martian weathering features in Tissint are compatible with the results of spacecraft observations of Mars, and Tissint has a cosmic ray dating exposure age of 0.7 ± 0.3 Ma—consistent with the reading of many other shergottites, notably EETA79001, suggesting that they were ejected from Mars during the same event.

The overall composition of the Tissint meteorite corresponds to that of aluminium-poor ferroan basaltic rock, which likely originated as a result of magmatic activity at the surface of Mars. These basalt then underwent weathering by fluids, which deposited minerals enriched in incompatible elements in fissures and cracks. A later impact on the surface of Mars melted the leached material forming black glassy veins. Finally shergottites were ejected from Mars about 0.7 million years ago.>>

[MarkBour]

If the earth is safe for the next 100 years, then what about Mars and Venus? If there were an impact on one of our neighbors, it would afford many interesting research possibilities.

Oh, the bitter irony if in the year 2084, a major impactor wiped out Elon's recently-achieved self-sustaining Mars colony.

[neufer]

We Now Know Exactly Which Crater the Martian Meteorites Came From
Universe Today, November 8, 2021 by Evan Gough

<<An impact on the red planet sent geological clues to Earth in the form of meteorites. The geological information contained in these meteorites would be even more valuable if we knew exactly where they came from. A team of researchers say they’ve figured it out.

According to a new study, the Martian meteorites came from Tooting crater, a large crater in Mars’ Tharsis region. The Tooting crater is 28 km in diameter and 1200 meters deep. It’s only a million years old, which is young for an impact crater.

Viking orbiter 1 image of Tooting

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<<Tooting is a 28 km wide impact crater (of the type rampart crater) with volcanic features at 23.1°N, 207.1°E, in Amazonis Planitia (Amazonis quadrangle), due west of the volcano Olympus Mons, on Mars. It was identified by planetary geologist Peter Mouginis-Mark in September 2004. Scientists estimate that its age is on the order of hundreds of thousands of years, which is relatively young for a Martian crater. A later study confirms this order of magnitude estimate.

Tooting is named after the London suburb of the same name. This is in accordance with the International Astronomical Union's rules for planetary nomenclature, which specify that craters on Mars less than 60 km in diameter should be named after "villages of the world with a population of less than 100,000". The discoverer named it after his home town because he "thought [his] mum and brother would get a kick out of having their home town paired with a land form on Mars". This caused a stir in the British press, with many well-known media outlets reporting on the issue.

The crater's youth was inferred from the lack of superimposed cratering, preserved impact melt in the crater, and that the central peak of the crater has not been buried by sediment.

Research published in the journal Icarus has found pits in Tooting Crater that are caused by hot ejecta falling on ground containing ice. The pits are formed by heat forming steam that rushes out from groups of pits simultaneously, thereby blowing away from the pit ejecta.

Due to the flatness of the surrounding lava flows (at 3872 m below Martian datum), it is possible to infer much about the crater's formation and ejecta blanket. For example, the volume of ejecta deposited from the formation of the crater is estimated to be 450 cubic kilometres and that this process took less than half an hour.>>

[johnnydeep]

We Now Know Exactly Which Crater the Martian Meteorites Came From
Universe Today, November 8, 2021 by Evan Gough

<<An impact on the red planet sent geological clues to Earth in the form of meteorites. The geological information contained in these meteorites would be even more valuable if we knew exactly where they came from. A team of researchers say they’ve figured it out.

According to a new study, the Martian meteorites came from Tooting crater, a large crater in Mars’ Tharsis region. The Tooting crater is 28 km in diameter and 1200 meters deep. It’s only a million years old, which is young for an impact crater.

Note that based on the Universe Today article, the conclusion isn't definitive. Crater 09-00015 is the other most likely possible source.

[neufer]

We Now Know Exactly Which Crater the Martian Meteorites Came From
Universe Today, November 8, 2021 by Evan Gough

<<An impact on the red planet sent geological clues to Earth in the form of meteorites. The geological information contained in these meteorites would be even more valuable if we knew exactly where they came from. A team of researchers say they’ve figured it out.

According to a new study, the Martian meteorites came from Tooting crater, a large crater in Mars’ Tharsis region. The Tooting crater is 28 km in diameter and 1200 meters deep. It’s only a million years old, which is young for an impact crater.

Note that based on the Universe Today article, the conclusion isn't definitive. Crater 09-00015 is the other most likely possible source.

The Tharsis mantle source of depleted shergottites revealed by 90 million impact craters
A. Lagain, G. K. Benedix, K. Servis, D. Baratoux, L. S. Doucet, A. Rajšic, H. A. R. Devillepoix, P. A. Bland, M. C. Towner, E. K. Sansom & K. Miljković
Nature Communications volume 12, Article number: 6352 (2021)

Tooting and 09-000015

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Abstract: The only martian rock samples on Earth are meteorites ejected from the surface of Mars by asteroid impacts. The locations and geological contexts of the launch sites are currently unknown. Determining the impact locations is essential to unravel the relations between the evolution of the martian interior and its surface. Here we adapt a Crater Detection Algorithm that compile a database of 90 million impact craters, allowing to determine the potential launch position of these meteorites through the observation of secondary crater fields. We show that Tooting and 09-000015 craters, both located in the Tharsis volcanic province, are the most likely source of the depleted shergottites ejected 1.1 million year ago. This implies that a major thermal anomaly deeply rooted in the mantle under Tharsis was active over most of the geological history of the planet, and has sampled a depleted mantle, that has retained until recently geochemical signatures of Mars’ early history.